Granulation of anammox microorganisms for autotrophic nitrogen removal from wastewater

Excessive discharge of nutrients in waters induces pollution such as such as eutrophication. Conventional methods to treat waters are expensive. Alternatively, anaerobic ammonium oxidation, termed anammox, has been recently developped with benefits such as low sludge production, 50% less aeration demand, no external carbon supply, 60% less power consumption, and 90% reduction of greenhouse gas emissions. However, anammox is limited by long start-up periods due to the low growth rate of anammox bacteria. This issue can be solved by complete retention of biomass by reactor modification or by formation of anammox granules. This article reviews the mechanisms of anammox granulation and biogranulation models. We present factors involved in the granulation processes such as hydrodynamic shear force, extracellular polymeric substances, hydraulic retention time, seed sludge and bioreactors. We also discuss the interaction of proteins and polysaccharides in anammox granules.